Provide a more general "Author" transaction for Differential

Summary:
Ref T13628. Currently, Differential has a "Commandeer" action, but no way to edit the author otherwise.

This is largely archaic: there is no reason to prevent editing the author, and this makes it difficult to undo mistakes if you commandeer by accident.

Instead, provide a normal "Author" field and a "Foist Upon" action, similar to the "Owner" and "Claim/Assign" fields in Maniphest.

Test Plan:
  - Applied author transactions as the old author ("foisted"), the new author ("commandeerd"), and an arbitrary third party ("changed author").
  - Tried to unassign author, etc.
  - Viewed stories in feed and transaction timeline.
  - Saw sensible automatic reviewer changes.
  - Used existing "Commandeer" action, which is unchanged.
  - Called "transaction.search" and saw reasonable transaction values.

Maniphest Tasks: T13628

Differential Revision: https://secure.phabricator.com/D21591

src/__phutil_library_map__.php

@@ -616,6 +616,7 @@ phutil_register_library_map(array(
     'DifferentialRevisionAuthorHeraldField' => 'applications/differential/herald/DifferentialRevisionAuthorHeraldField.php',
     'DifferentialRevisionAuthorPackagesHeraldField' => 'applications/differential/herald/DifferentialRevisionAuthorPackagesHeraldField.php',
     'DifferentialRevisionAuthorProjectsHeraldField' => 'applications/differential/herald/DifferentialRevisionAuthorProjectsHeraldField.php',
+    'DifferentialRevisionAuthorTransaction' => 'applications/differential/xaction/DifferentialRevisionAuthorTransaction.php',
     'DifferentialRevisionBuildableTransaction' => 'applications/differential/xaction/DifferentialRevisionBuildableTransaction.php',
     'DifferentialRevisionCloseDetailsController' => 'applications/differential/controller/DifferentialRevisionCloseDetailsController.php',
     'DifferentialRevisionCloseTransaction' => 'applications/differential/xaction/DifferentialRevisionCloseTransaction.php',
@@ -6727,6 +6728,7 @@ phutil_register_library_map(array(
     'DifferentialRevisionAuthorHeraldField' => 'DifferentialRevisionHeraldField',
     'DifferentialRevisionAuthorPackagesHeraldField' => 'DifferentialRevisionHeraldField',
     'DifferentialRevisionAuthorProjectsHeraldField' => 'DifferentialRevisionHeraldField',
+    'DifferentialRevisionAuthorTransaction' => 'DifferentialRevisionTransactionType',
     'DifferentialRevisionBuildableTransaction' => 'DifferentialRevisionTransactionType',
     'DifferentialRevisionCloseDetailsController' => 'DifferentialController',
     'DifferentialRevisionCloseTransaction' => 'DifferentialRevisionActionTransaction',

src/applications/differential/editor/DifferentialRevisionEditEngine.php

@@ -176,6 +176,23 @@ final class DifferentialRevisionEditEngine
       ->setConduitTypeDescription(pht('New revision title.'))
       ->setValue($object->getTitle());
 
+    $author_field = id(new PhabricatorDatasourceEditField())
+      ->setKey(DifferentialRevisionAuthorTransaction::EDITKEY)
+      ->setLabel(pht('Author'))
+      ->setDatasource(new PhabricatorPeopleDatasource())
+      ->setTransactionType(
+        DifferentialRevisionAuthorTransaction::TRANSACTIONTYPE)
+      ->setDescription(pht('Foist this revision upon someone else.'))
+      ->setConduitDescription(pht('Foist this revision upon another user.'))
+      ->setConduitTypeDescription(pht('New author.'))
+      ->setSingleValue($object->getAuthorPHID());
+
+    if ($viewer->getPHID() === $object->getAuthorPHID()) {
+      $author_field->setCommentActionLabel(pht('Foist Upon'));
+    }
+
+    $fields[] = $author_field;
+
     $fields[] = id(new PhabricatorRemarkupEditField())
       ->setKey(DifferentialRevisionSummaryTransaction::EDITKEY)
       ->setLabel(pht('Summary'))

src/applications/differential/editor/DifferentialTransactionEditor.php

@@ -198,7 +198,7 @@ final class DifferentialTransactionEditor
         ->setNewValue($want_downgrade);
     }
 
-    $is_commandeer = false;
+    $new_author_phid = null;
     switch ($xaction->getTransactionType()) {
       case DifferentialRevisionUpdateTransaction::TRANSACTIONTYPE:
         if ($this->getIsCloseByCommit()) {
@@ -239,12 +239,22 @@ final class DifferentialTransactionEditor
         break;
 
       case DifferentialRevisionCommandeerTransaction::TRANSACTIONTYPE:
-        $is_commandeer = true;
+        $new_author_phid = $actor_phid;
         break;
+
+      case DifferentialRevisionAuthorTransaction::TRANSACTIONTYPE:
+        $new_author_phid = $xaction->getNewValue();
+        break;
+
     }
 
-    if ($is_commandeer) {
-      $results[] = $this->newCommandeerReviewerTransaction($object);
+    if ($new_author_phid) {
+      $swap_xaction = $this->newSwapReviewersTransaction(
+        $object,
+        $new_author_phid);
+      if ($swap_xaction) {
+        $results[] = $swap_xaction;
+      }
     }
 
     if (!$this->didExpandInlineState) {
@@ -1472,21 +1482,25 @@ final class DifferentialTransactionEditor
     return $this;
   }
 
-  private function newCommandeerReviewerTransaction(
-    DifferentialRevision $revision) {
+  private function newSwapReviewersTransaction(
+    DifferentialRevision $revision,
+    $new_author_phid) {
 
-    $actor_phid = $this->getActingAsPHID();
-    $owner_phid = $revision->getAuthorPHID();
+    $old_author_phid = $revision->getAuthorPHID();
 
-    // If the user is commandeering, add the previous owner as a
-    // reviewer and remove the actor.
+    if ($old_author_phid === $new_author_phid) {
+      return;
+    }
+
+    // If the revision is changing authorship, add the previous author as a
+    // reviewer and remove the new author.
 
     $edits = array(
       '-' => array(
-        $actor_phid,
+        $new_author_phid,
       ),
       '+' => array(
-        $owner_phid,
+        $old_author_phid,
       ),
     );
 
@@ -1503,6 +1517,7 @@ final class DifferentialTransactionEditor
       ->setNewValue($edits);
   }
 
+
   public function getActiveDiff($object) {
     if ($this->getIsNewObject()) {
       return null;

src/applications/differential/xaction/DifferentialRevisionAuthorTransaction.php

@@ -0,0 +1,155 @@
+<?php
+
+final class DifferentialRevisionAuthorTransaction
+  extends DifferentialRevisionTransactionType {
+
+  const TRANSACTIONTYPE = 'differential.revision.author';
+  const EDITKEY = 'author';
+
+  public function generateOldValue($object) {
+    return $object->getAuthorPHID();
+  }
+
+  public function generateNewValue($object, $value) {
+    return $value;
+  }
+
+  public function applyInternalEffects($object, $value) {
+    $object->setAuthorPHID($value);
+  }
+
+  public function validateTransactions($object, array $xactions) {
+    $actor = $this->getActor();
+    $errors = array();
+
+    if (!$xactions) {
+      return $errors;
+    }
+
+    foreach ($xactions as $xaction) {
+      $old = $xaction->generateOldValue($object);
+      $new = $xaction->getNewValue();
+
+      if ($old === $new) {
+        continue;
+      }
+
+      if (!$new) {
+        $errors[] = $this->newInvalidError(
+          pht('Revisions must have an assigned author.'),
+          $xaction);
+        continue;
+      }
+
+      $author_objects = id(new PhabricatorPeopleQuery())
+        ->setViewer($actor)
+        ->withPHIDs(array($new))
+        ->execute();
+      if (!$author_objects) {
+        $errors[] = $this->newInvalidError(
+          pht('Author "%s" is not a valid user.', $new),
+          $xaction);
+        continue;
+      }
+    }
+
+    return $errors;
+  }
+
+  public function getIcon() {
+    $author_phid = $this->getAuthorPHID();
+    $old_phid = $this->getOldValue();
+    $new_phid = $this->getNewValue();
+
+    $is_commandeer = ($author_phid === $new_phid);
+    $is_foist = ($author_phid === $old_phid);
+
+    if ($is_commandeer) {
+      return 'fa-flag';
+    }
+
+    if ($is_foist) {
+      return 'fa-gift';
+    }
+
+    return 'fa-user';
+  }
+
+  public function getColor() {
+    return 'sky';
+  }
+
+  public function getTitle() {
+    $author_phid = $this->getAuthorPHID();
+    $old_phid = $this->getOldValue();
+    $new_phid = $this->getNewValue();
+
+    $is_commandeer = ($author_phid === $new_phid);
+    $is_foist = ($author_phid === $old_phid);
+
+    if ($is_commandeer) {
+      return pht(
+        '%s commandeered this revision from %s.',
+        $this->renderAuthor(),
+        $this->renderOldHandle());
+    }
+
+    if ($is_foist) {
+      return pht(
+        '%s foisted this revision upon %s.',
+        $this->renderAuthor(),
+        $this->renderNewHandle());
+    }
+
+    return pht(
+      '%s changed the author of this revision from %s to %s.',
+      $this->renderAuthor(),
+      $this->renderOldHandle(),
+      $this->renderNewHandle());
+  }
+
+  public function getTitleForFeed() {
+    $author_phid = $this->getAuthorPHID();
+    $old_phid = $this->getOldValue();
+    $new_phid = $this->getNewValue();
+
+    $is_commandeer = ($author_phid === $new_phid);
+    $is_foist = ($author_phid === $old_phid);
+
+    if ($is_commandeer) {
+      return pht(
+        '%s commandeered %s from %s.',
+        $this->renderAuthor(),
+        $this->renderObject(),
+        $this->renderOldHandle());
+    }
+
+    if ($is_foist) {
+      return pht(
+        '%s foisted %s upon %s.',
+        $this->renderAuthor(),
+        $this->renderObject(),
+        $this->renderNewHandle());
+    }
+
+    return pht(
+      '%s changed the author of %s from %s to %s.',
+      $this->renderAuthor(),
+      $this->renderObject(),
+      $this->renderOldHandle(),
+      $this->renderNewHandle());
+
+  }
+
+  public function getTransactionTypeForConduit($xaction) {
+    return 'author';
+  }
+
+  public function getFieldValuesForConduit($object, $data) {
+    return array(
+      'old' => $object->getOldValue(),
+      'new' => $object->getNewValue(),
+    );
+  }
+
+}

src/applications/maniphest/xaction/ManiphestTaskOwnerTransaction.php

@@ -127,8 +127,7 @@ final class ManiphestTaskOwnerTransaction
 
       if (!$assignee_list) {
         $errors[] = $this->newInvalidError(
-          pht('User "%s" is not a valid user.',
-          $new));
+          pht('User "%s" is not a valid user.', $new));
       }
     }
     return $errors;